TUNIS, Tunisia — Radical militants killed four members of the National Guard in the mountainous Kasserine region near the Algerian border, Tunisia's Interior Ministry said Wednesday.

Ministry spokesman Mohammed Ali Aroui said 20 militants from the Oqba Ibn Nafaa radical group ambushed a night patrol around 20 kilometers (12 miles) from the Kasserine city around midnight.

"Our response will be strong and violent," he said, adding that a sweep of the area was underway to catch the attackers.

The attack took place near Mount Chaambi, a national park on the Algerian border that has provided refuge to al-Qaida linked Islamist radicals blamed for attacks against army and politicians in Tunisia for the past two years.

The attack comes as Tunisian forces on the Libyan border are on high alert in the wake of the murder of 21 Egyptian Christians in Libya by another radical Islamic group.

Since Tunisians overthrew their secular dictator in 2011, kicking off the region-wide Arab Spring, they have come increasingly under attack by Islamic militants.

Despite the efforts of Tunisia's small army, attacks have continued around Mount Chaambi.

The Oqba bin Nafaa group describes itself as the military wing of Ansar al-Sharia, whose leaders fled to Libya in 2013. They have been implicated in the murder two politicians in 2013, the massacre of 15 soldiers last July and an attack on the home of the former interior minister.

Aroui said the attack must be in revenge for a series of police operations against jihadi "sleeper cells" that have resulted in the arrest of dozens of suspected militant supporters. In one sweep earlier this month, 32 suspects were arrested for planning attacks on the Interior Ministry and National Guard bases.

Algerian and Tunisian forces are attempting to coordinate their efforts to control the rugged region, which straddles the border between the two countries.

On Monday, Algerian forces killed a militant carrying explosives near Tebessa, just across the border from Kasserine.